Highly emissive cathode



Jan. 10, 1933. o. EMERSLEBEN HIGHLY EMISSIVE CATHODE Filed June 22, 1931 .7/21 for: 9% a.

OTTO EMEBSLEBEN, F BERLIN, GERMANY HIGHLY EMISSIVE OATHODE Application filed June 22, 1931, Serial No. 545,998, and. in Germany June 25, 1930.

The invention relates to a highly emissive with a hydroxyl group). Barium sulphide cathode'and a method ofproducing the same, 'BaS orbarium cyanide (Ba(CN) are exmore particularly according to the metal vaamples of those compounds which result in pour process. In cathodes which are prothe necessary mutual decompositions with 5 duced according to this method, for example the barium. The electrical conductivity, 50

by the fine application of barium vapour to which more particularly in the case of barium a cathode composed of another material, the sulphide is greater than that with barium oxextremely high emission of the applied bariide, is apparently the reason for more favour- ,um is based on the co-operation of a number able emissive conditions.

of factors, which in themselves have not as The invention will therefore be described 55 yet been fully accounted for, but in which a in the following with the assistance of a few temporary oxidation of the barium appears examples based on the use of barium sulphide to have considerable hearing. The condion the cathode. The most simple emboditions are possibly u h th t. electrglytical or ment of a method of production of cathodes similar conversions occur between metallic of this description would consist in applybarium and barium oxide in the known valves ing barium sulphide to the cathode in direct with bariumemission, and that the electronic fashion, and thereupon atomizing barium on emission takes place upon a reaction of this to the cathode in any suitable manner known kind, for example upon the oxidation of the per se. In place of the direct employment barium or the reduction of the barium oxide. 0i3 b m sulphide it may be desirable to in- It has also been shown that heretofore cerr uce ulphur vapour in minute amount, tain substances have always been present pereither pr or to or immediately after the atmitting of the oxidation of the barium. It omlzation of the barium, in order to thus obwas shown, for example, that tungsten filatam the formation of sulphide.

t hi l1 contain certain oxides, are quite According, however, to the additional sub- 70 particularly adapted to serve as body mate- Ject matter of the invention, the sulphide is rials for highly emissive barium cathodes. produced on the cathode itself. In this man- The inv ntion relates to another method ner gas-technical, vacuum-technical and oth of activating the barium emission which has er difliculties in manufacture are avoided.

proved to be of advantage, and which, ac- It is known in itself that barium sulphide, 7

cording to the tests hitherto carried out, llaS, is obtained by the reduction of barium would appear to be superior in many respects sulphate, 1321550. If now barium sulphate is to the formation by oxidation. applied to the filament, and on the other It is unnecessary for the barium to be oxihand, in the manner known per se and cusdized. In addition to barium oxide otherbartoniary in respect of the metal vapour process, ium compounds have proved to be at least barium is so atomized within the valve that equivalent in an electrical respect, while these the same is deposited preferably on the filabarium compounds of other kind disclose adm-ent, this barium itself will act as reducing vantages both as regards the method as well agent in face of the barium sulphate, possibly 49 as certain conditions of emission. according to the following formula, which is 5" According to the invention, compounds of at least correct in the final result: that kind are employed on the cathode which 2 do not contain the metal in combination with BasOf+iBa oxygen alone (or, which in a certain respect The invention is not limited to the use of 4 is equivalent thereto, in combinationsolely barium alone. Similar substances may also socket of the discharge vessel.

be employed as emissive metals for performing the metal vapour process and as cations for the sulphate. Thus, for example, potas sium sulphate is more suitable than barium sulphate for application to the cathode, particularly if the same is employ d in the form of potassium bisulphate, KHSOi, which possesses a considerably lower melting point than neutral potassium sulphate.

Good results are accordingly obtained with a cathode produced in the following manner:

A tungsten filament was in the first place conducted through molten potassium bisulphate produced at 2lO-300 so that the same was coated therewith on the surface. After setting the filament in the system and fitting the system in the valve, the hydrogen was removed trom the sulphate, for example during the pumping operation, by heating the filament, so that as a whole merely normal sulphate apparently remained on the filament. surface. Barium was thereupon atomized on to the cathode, a barium oxide and aluminium mixture bein applied laterally of the oath ode and heated to the extent of aluminothermal reaction. The barium deposited on the cathode will undoubtedly have reduced the potassium sulphate. Presumably there is formed in this connection an equilibrium of potassium sulphide K 8, barium sulphide BaS, barium oxide Bat) and potassium oxide K 0, in the presence of a considerable excess of metallic barium.

The smallness of the amounts decomposed upon these reactions, and in part only requiring to be present in layers of atomary thickness, did not permit of investigations as to whether all of these assumed components of the reaction actually occurred. It is in any case quite certain that cathodes produced ac cording to the method described disclose an admirable barium emission, without in this connection there being necessary as a particular step in the method the oxidation particularly made use of in the usual process.

A further embodiment of the process according to the invention may consist in s phurating the applied barium by the introduction of small quantities of sulphuretted hydrogen. In this case there is formed barium sulphide, while upon the degasifying process not only the excessive sulphurctted hydrogen but also the gases, such as hydrogen, formed upon the reaction may be pumped away. The method is performed in the most suitable manner by at first atomizing a small quantity of barium on to the cathode, then introducing a-small quantity of sulphuretted hydrogen, for example from a sulphuretted hydro gen container, which by means of a three-way tap is connected in a manner permitting the same to be readily shut ofi with the pumping After the introduction of the sulphuretted hydrogen and the subsequent removal of the excess. by pumping, the valve is preferably first sealed and then barium again evaporated, viz., at this stage the essential part of the barium.

Those electrodes which are not desired to perform emission, i. e., in normal threeelectrode 'alves all electrodes with the exception of the cathode, are in this case preferably produced from a metal of that kind which is not, or only to the least possible extent, attached by the sulphuretted hydrogen.

Admirably adapted for this purpose is molybdenum, which in itself is already employed a material for the grids, but which in the present case, according to the additional subject matter of the application, also enters with advantage into consideration as regards a material for the anode. Tungsten may also be employed for electrodes of this kind, whether the same is pure or in the form of an addition or accompanied by additions, which should not be attacked in carrying out the process according to the invention.

An additional embodiment of the invention consists in introducing sulphur dioxide S0 into the valve. This possesses in comparison with sulphuretted hydrogen the advantage of not being so very highly reactive. The same does not attack the metals in the valve with the same readiness. It is possible, for xample, without difficulty, to employ nickel electrodes, and more particularly nickel anodes, in those valves into which sulphur dioxide is temporarily introduced in performance of the process according to the invention. The sulphur dioxide is mutually decomposed *ith barium oxide in such fashion that equilibrium exists between these two substances on the one hand and barium sulphate and barium sulphide on the other hand. In turn the barium sulphate, in the manner set forth at the commencement, results by reason of reduction by metallic barium in barium sulphide and new barium oxide. Small amounts of barium oxide, which initially are always present if due only to inexactitudes or leakages of the apparatus, are accordingly sufiicient to create fresh quantities of barium oxide which, for the additional course of the process, are essential for maintaining the formation of barium sulphide (in addition to barium oxide) from 1 arium and sulphur dioxide.

Altogether, there accordingly results from the two reactions, via,

(1) lSO +4BaO=BaS -l ZlBaSO and (2) BaSOfi- 413a =BaS 4BaO a mutual decomposition according to the total equation (3) 3Ba+ SO =BaS +2BaO In this manner there accordingly results reeaess a cathode which, in addition to barium sulphide, also contains barium oxide. It would seem, however, that the barium sulphide, due to its greater conductivity, also in this case plays a predominating part in the electronic emission. The invention has been described substantially with the assistance of a few examples of the metal vapour process, which refer to the use of barium cathodes, because among the metal vapour cathodes these are the most important. The invention, however, is not restricted thereto, and may, with correspondingly adapted possibilities of reaction, which in part are somewhat difi'erent in the case of the other materials, be applied to cathodes making use of other light metals, more particularly cathodes composed of calcium or strontium.

he invention has also been more particularly described with the use of bivalent sulphur as electron transmitter. To this the invention is also in no way confined.

The invention is illustrated by the accompanying drawing in which Figure 1 shows an electron discharge device containing a plate 1, a grid 2 and a cathode 3. A long tudinal sect on through this cathode 3 is shown on a larger scale in Figure 2. The cathode consists of the cathode body li. e. a wire of tungsten or like metals and the actual emissive layer 5 for instance of barium. Between the wire l and the layer 5 an intermediate layer is provided consisting each according to the selection of the starting material of barium sulphides, barium oxides, etc.

I claim:

1. A method for manufacturing highly emissive cathodes which consists in coating the surface of the cathode body with a compound of sulphur with a highly emissive metal and that thereon a highly emissive ubstance is deposited in form of metal vapour.

2. A method for manufacturing highly emissive cathodes which consists in coating the cathode body with a compound of sulphur with a highly emissive metal adapted to produce by reactions sulphides of said highly emissive metal and that thereon a highly emissive substance is deposited in form of metal vapour.

3. A. method for manufacturing highly emissive cathodes which consists in coating the cathode body with a compound of sulphur with earth-alkali metals adapted to produce by reactions sulphides of said earthalkali metals and that thereon a highly emissive substance is deposited in form of metal vapour.

4. A method for manufacturing highly emissive cathodes which consists in coating the cathode body with a sulphate of earthalkali metals and that thereon a highly emis- OTTO EMERSLEBEN. 

